Fix EZP-22664: Additional fix for CacheThreshold not being observed.

Additional fix for https://jira.ez.no/browse/EZP-22664 (PR #938)

This PR actually removes the node cache clearing logic from both `eZContentCacheManager::clearObjectViewCache()` and `eZContentCacheManager::clearObjectViewCacheArray()`, 
and adds a new function `clearNodeViewCacheArray()`, which prevents code duplication and helps maintainability.